You choose how the counters will be distributed as you put Verdurous Gearhulk’s triggered ability onto the stack. Each target creature must be assigned at least one counter.

9/20/2016

If one of the target creatures becomes an illegal target in response to Verdurous Gearhulk’s triggered ability, the +1/+1 counters that would have been put on that creature are lost. They can’t be put on another legal target.